1. Field of the Invention
The present invention relates to a negative ion generating apparatus for generating a high density of negative ion particles, which can be used for the sterilization of foods, drinking water, rooms for living, or for clearing the air in a space. In this specification and claims, the phrase "negative ion" means a gas containing negatively ionized particles.
2. Description of the Prior Art
Various apparatus using active particles, for example, ionized particles or ozone, have been already developed in the prior art, for preventing the propagation of bacteria, cleaning of the air in a space, or for deodorization.
A negative ion generating apparatus takes in oxygen, and other gases into the apparatus, and generates a discharge to ionize the molecules in the gas, by imposing a high voltage, which is called a "corona discharge phenomenon", and produces negatively ionized particles. The gas containing the negatively ionized particles together with ozone gas etc is supplied to a space in which objects are treated by the negatively ionized particles so as to prevent the propagation of bacteria, clean the air therein, deodorize etc.
FIG. 9 shows a cross sectional view of a negative ion generating apparatus known in the prior art, shown along the direction of the gas flow. The reference numeral 1 denotes a power supply 2 is a discharge electrode comprised of a plurality of parallel thin metal wires, which are electrically connected with the power supply 1. 3 is a ground electrode comprised of metal grid or mesh metal plate, which is arranged to face the discharge electrode. The power supply supplies negative pulses of some kilovolts to the discharge electrode. 4 is a ventilator, for example, an electric fan. 25 is an air passage, through which the air drawn by the ventilator passes. 9 is an air inlet, through which the air is taken in. 12 is a discharge space or discharge chamber between the discharge electrode 2 and ground electrode 3, in which the air is ionized. The ionized gas containing negative ion particles passes through the grid or mesh plate of the ground electrode 3, to be radiated on the objects to be sterilized and so on. In this specification and claims, the space or the chamber, in which such objects to be sterilized are disposed, is called an "object space".
The functioning of the negative ion generating apparatus of the prior art is explained below.
The ventilator (electric fan) 4 takes in a gas, preferably air, from the exterior space into the apparatus, and urges the gas to move towards the object space through the discharge electrode 2 and ground electrode 3. Hence a gas flow arises in the apparatus from the upstream to the downstream direction. Negative pulses of some kilovolts are supplied to the thin wires of the discharge electrode 2 from the power supply 1. This causes a corona discharge between the negatively charged discharge electrode 2 and the ground electrode 3. It is understood, in general, that there is only one discharge point in the thin wires, for every one pulse where the corona discharge occurs, such point being called a "corona discharge point".
In a corona discharging area, electrons combine with gas particles (especially with oxygen molecules), which are found near to the discharge electrode 2, to generate negative ion particles. Simultaneously, a small quantity of ozone can be generated, as a result of collision and dissociation of negative ionized particles, which are originated from the oxygen molecules. The gas containing the negative ion particles, which are generated at an area near to the discharge electrode 2, in such a manner, is driven to flow into the object space, which is found in the downstream area, after passing through the grid wires or a mesh plate of the ground electrode, by the blowing force of the ventilator ( for example, an electric fan). The negative ions can be used for preventing the propagation of the bacteria, for example.
In another expression, the ventilator 4 sucks the air from the exterior through the inlet 9, and the air is sent to the discharge space 12 through the air passage 25. A high voltage from the power supply 1 is imposed on the discharge electrode 2, which causes corona discharges in the discharge space 12 between the ground electrode 3 and the discharge electrode. The negatively ionized particles, for example, O.sup.2- particles, generated in the corona discharges move towards the ground electrode 3. The ionized gas is blown out from the electrode portion towards the exterior of the apparatus, by the blowing force of the ventilator 4.
As shown in FIG. 9, the discharge chamber 12 in the prior art that the air flows through has a constant cross section in its whole region from upstream to downstream. Thus, when the capacity of the electric fan 1 is constant, the flow velocity is constant. As a result, the generating rate of negative ion particles per unit time and the supplying rate of negative ion particles per unit time are constant.
A gas flow direction deflecting board 6, as shown in FIG. 10, is disclosed in the prior art, for controlling the flow direction, and for increasing the negative ion particle generating rate per unit time, by increasing the flow velocity at the area near to the discharge electrode.
In the negative ion generating apparatus in the prior art having such a structure, a large portion of the generated negative ion particles tend to move towards the grid wires or mesh plate of the ground electrode 3 and to be absorbed therein, because of their negative charges. Consequently, there is a problem that only a small number of the negative ions can pass through the grid wires or mesh plate.
In the negative ion generating apparatus of the prior art, the supplying capacity of the negative ion particles to the object space, after their generation in the region near to the discharge electrode, is determined by the capacity of an electric fan. Thus, an augmentation of the fan capacity is required to increase the density of the negative ion particles in the object space, which leads, in turn, to the problem of the increase of the electric power consumption.
Although the flow direction control member, as shown in the prior art, is effective regarding of the control of the flow direction and the speeding up of the air flow, it entails the problems that the flow direction control member, which is perpendicular to the flow direction, causes a loss of pressure head of the air flow. Additionally, the flow direction control member shall be arranged at an upstream position of the discharge electrode, spaced some distance, for avoiding the blunting of the electric field by it. Thus, even if the velocity of the flow is increased by the member, the velocity is decreased at the region of the discharge electrode, when it arrives there. Consequently, there is a problem that the negative ion particles can not be generated effectively. Another problem is that the number of member parts of the apparatus increases, and the size of the apparatus further becomes large.
Moreover, there is a requirement regarding environmental standards which requires that the density of ozone simultaneously generated together with the negative ion particles shall be under 0.1 ppm.
The negative ion generating apparatus in the prior art has further drawbacks as follows:
The discharge electrode is comprised of thin wires disposed in parallel, thus there is a limitation in the number of the electrodes disposable in an unit area, avoiding interference between the discharge electrodes. On the other hand, the number of the electrodes corresponds to the number of corona discharges per unit area.
The thin wires, which are pulled from both sides, have a tendency to easily break due to the high voltage applied thereon.
The direction of the corona discharges is substantially parallel to the flow direction of the gas, thus, the generated negative ion particles, are easily caught by the ground electrode, which is a mesh plate.
Thus the supply efficiency of the generated negative ion particles into the object space is small.
Finally, the size of the apparatus is large.
The present invention eliminates the drawbacks of the negative ion generating apparatus of the prior art.